The present invention relates to the manufacture of transparent bodies to be used in the windows of land, sea, or air vehicles.
In particular, the present invention relates to the manufacture of such transparent bodies with predetermined optical density or opacity gradients.
Thus, the present invention relates to the art of manufacturing light filters by applying to the surface of a transparent substrate or body a light filtering coating in the form of a light filtering substance which is deposited on the substrate or body by thermal evaporation in an evacuated atmosphere. The invention relates particularly to the method of providing such light filters with a varying optical density.
Thus, the method of the present invention may be employed in the manufacture of light-filtering glass panes or panels to be used in the windows or portholes of vehicles which are designed to travel on the ground or to be water-borne or air-borne.
While of course such transparent bodies having predetermined optical density gradients are well-known, the known methods of thermally evaporating in an evacuated atmosphere depositions which will form coatings of varying thickness to achieve the optical density gradient suffer from serious drawbacks. It is customary with conventional methods to emply various types of baffles, shutters, masking members, or the like, which are moved in a predetermined manner during the deposition of the coating on the surface of the transparent body, or with subsequent selective oxidation of the deposited coating being achieved by way of an electrical discharge. Thus, these known techniques require situating in the evacuated chamber where the deposition of the coating takes place movable structures which undesirably complicate the method of manufacture while increasing the cost thereof considerably.